pd.py

import random

def utility(s1, s2):
    if s1 == s2 == 'B':
        return 4,4
    if s1 == s2 == 'C':
        return 2,2
    if s1 == 'C' and s2 == 'B':
        return 5,0
    return 0,5

p1strategies = []
p2strategies = []
utilities = [(0,0)]

# Two players playing randomly
while len(p1strategies) < 5:
    p1strategies.append(random.choice(['B', 'C']))
    p2strategies.append(random.choice(['B', 'C']))
    thisround = utility(p1strategies[-1], p2strategies[-1])
    utilities.append((utilities[-1][0] + thisround[0], utilities[-1][1] + thisround[1]))
    print '--------'
    print p1strategies
    print p2strategies
    print utilities


print 50 * "="
# One player playing tit for tat

def tit_for_tat(s1):
    if s1 == 'B':
        return 'B'
    return 'C'

p1strategies = []
p2strategies = []
utilities = [(0,0)]

while len(p1strategies) < 5:
    p1strategies.append(random.choice(['B', 'C']))
    if len(p2strategies) == 0:
        p2strategies.append('C')
    else:
        p2strategies.append(tit_for_tat(p1strategies[-2]))
    thisround = utility(p1strategies[-1], p2strategies[-1])
    utilities.append((utilities[-1][0] + thisround[0], utilities[-1][1] + thisround[1]))
    print '--------'
    print p1strategies
    print p2strategies
    print utilities